This invention relates to a process for reducing the amount of decomposition products released from a Type II anion exchange resin in the hydroxide form, and it also relates to the resin prepared by this method.
Strongly basic, Type 11 quaternary ammonium resins are used primarily for water treatment applications, often in mixed bed ion exchange units. Examples of water treatment applications include the following: (1) dealkalizing softened water for make-up to boiler feeds and cooling towers, (2) reducing sulfate or nitrate in water supplies, (3) deionizing water supplies, and (4) removing oxygen from deionized water.
Type 11 resins in the chloride form typically exhibit excellent stability. Unfortunately, Type II resins regenerated with caustic and used in the hydroxide form are inherently less stable than Type II resins in the chloride form or strong base Type I resins, and therefore are often limited to certain applications requiring temperatures no greater than ambient. The decrease in stability for the hydroxide form resins has been linked to the release of decomposition products, primarily acetaldehyde, during use or storage. See, for example, Water Quality Association's Draft Response to the Environmental Protection Agency, Aug. 28,1987.
For users who regenerate with caustic, the choice between using a Type II resin in the hydroxide form or a strong base Type I resin for water treatment often depends on economics and the particular application. Type II resins offer greater ease of regeneration than Type I resins, but their regeneration efficiency can be counterbalanced by their relative chemical instability. Therefore, the preparation of a Type II resin in the hydroxide form that exhibits excellent stability during use or storage would overcome a significant disadvantage that these resins currently possess.